The field is that hydraulic engineering needed to guide, regulate, and modify fluid flow. In particular, a preferred embodiment of the present invention assists waterborne fauna, such as fish, in avoiding contact with a manmade obstruction.
Water resources development typically includes the construction of dams across rivers to impound and regulate flows for power production, flood control, water supply, irrigation and other economically beneficial uses of water. In many rivers, adult fish typically migrate upstream through the river to spawn and rear in upstream areas. Once young, or juvenile, fish reach a certain size they instinctively migrate downstream to the adult habitat areas in downstream reaches of the river, in lakes, or in the ocean where they mature into adults and complete their life cycle. Juvenile salmon and many other juvenile fishes are spawned in upstream fresh water systems where early life stages are completed but reach adulthood in downstream areas.
Unfortunately, dams block the migration of fish and thereby interfere with the completion of their natural life cycles. Sustainable water resources development is often facilitated by the use of hydraulic structures to pass these juvenile fish around the dam and other channel obstructions.
Systems and methods for assisting fish in circumventing man-made barriers in streams have been tried for many years, e.g., U.S. Pat. No. 3,338,056, Fingerling Saving System, issued to Roscoe, Aug. 29, 1967, details a complex arrangement of recesses using vertically oriented entrances for permitting the transport of fingerlings around a dam. Quoting from the ""056 patent: xe2x80x9cThe difficulty (of getting fingerlings downstream) arises due to the tendency of the fingerlings to follow flowing currents of water, and ordinarily such flowing currents go through the turbines of the associated power station. The fingerlings suffer high mortality in passing through the turbines. . . .xe2x80x9d
A later patent, U.S. Pat. No. 4,437,431, Method and Apparatus of Diversion of Downstream Migrating Anadromous Fish, issued to Koch, Mar. 20, 1984, uses an xe2x80x9cartificial streamxe2x80x9d generated by water jets within the natural stream together with long tubes having funnel-shaped entrances located on the sides of the stream at some distance from the upstream side of the dam. Another solution that offers an xe2x80x9cattractingxe2x80x9d artificial current based on an active source include a propeller generated current as described in U.S. Pat. No. 6,102,619, Flow Inducer Fish Guide and Method of Using Same, issued to Truebe et al., Aug. 15, 2000. A related technique involving a series of opening and closing valves, fish passing actuators and conduits is detailed in U.S. Pat. No. 6,273,639 B1, Method and Apparatus for Facilitating Migration of Fish Past Dams and Other Barriers in Waterways, issued to Eikrem et al., Aug. 14, 2001.
To comply with government regulations, other solutions have involved configurations of barrier screens and bypass conduits such as that envisioned by U.S. Pat. No. 4,481,904, Fish Conservation Device, issued to Fletcher, Nov. 13, 1984; U.S. Pat. No. 4,526,494, Penstock Fish Diversion System, issued to Eicher, Jul. 2, 1985; and U.S. Pat. No. 4,740,105, issued to Wollander, Apr. 26, 1988. One such screen barrier uses a number of like modules in a ladder arrangement affixed to the bottom of the channel as described in U.S. Pat. No. 4,929,122, Fish Protection System for Dams, issued to Yoas, May 29, 1990. An underwater xe2x80x9cscreen housexe2x80x9d located adjacent a dam is described in U.S. Pat. No. 5,385,428, Water Intake Fish Diversion Apparatus, issued to Taft et al., Jan. 31, 1995. A buoyant screen that may be sunk and raised at appropriate fish migrations times is described in U.S. Pat. No. 5,558,462, Flat Plate Fish Screen System, issued to O""Haver, Sep. 24, 1996.
Still other solutions provide for a buoyant arrangement of vertically oriented slats located some distance upstream from a barrier such as described in U.S. Pat. No. 5,263,833, Fish Guiding Assembly and Method Utilizing Same, issued to Robinson et al., Nov. 23, 1993. This arrangement, and others like it, consumes a considerable amount of the surface area immediately upstream from the dam.
Active solutions are also proposed as exemplified in U.S. Pat. No. 5,445,111, Electrified Fish Barriers, issued to Smith, Aug. 29, 1995, describing linear curtain arrays characterized by pulsed driving signals that may use varying voltages. Other active solutions include complex electronic detectors and control systems to alter the operation of a hydroelectric powerhouse in the presence of migrating fish as described in U.S. Pat. No. 6,038,494, Control System for Enhancing Fish Survivability in a Hydroelectric Power Generation Installation, issued to Fisher et al., Mar. 14, 2000.
Fish ladders have been used to help returning anadromous fish get to spawning beds and are also proposed to help the juveniles return to the sea as described in U.S. Pat. No. 6,155,746, Fish Ladder and Its Construction, to Peters, Dec. 5, 2000. This details a complex series of basins having vertical inflow and outflow slots for transporting fish around a barrier.
The above solutions involve a configuration that is either much more complex and costly than a preferred embodiment of the present invention, uses much more xe2x80x9cgeographyxe2x80x9d to effect the desired result, uses energy or large quantities of water to effect the desired result, is unable to be used to modify an existing barrier, or a combination of these undesirable factors.
Juvenile outmigrating fish instinctively seek passage through the dam when their downstream journey is blocked. For a detailed discussion, refer to U.S. Pat. No. 6,160,759, Method for Determining Probable Response of Aquatic Species to Selected Components of Water Flow Fields, issued to Nestler et al., Dec. 12, 2000, and incorporated herein by reference. In the Columbia River, conventional surface bypass collectors (SBC""s) are a preferred passage design used at dams for passing outmigrating juvenile fish.
A conventional SBC employs a water intake plume to attract fish to its entrance. Using conventional engineering concepts, the SBC""s attract and concentrate fish for conveyance around the dam in a manner that helps prevent their entry into turbines or other high-energy hydraulic conditions where they may be injured or killed. An SBC uses an attracting intake plume of sufficient flow magnitude to overcome the attracting flow of competing inflows such as are present at hydroturbines, sluicegates or spillways. Once juvenile fish enter the SBC they are conveyed to a bypass channel where they continue the migration downstream of the dam. Design of the entrance hydraulic conditions used in conventional SBCs does not incorporate knowledge of the behavior of the juvenile fish in natural streams and rivers. As a consequence, the performance of conventional SBCs varies, with some working well and others not. Poor performance most commonly results from uncertainty about the flow conditions required to attract juvenile fish to the entrance of the SBC. A preferred embodiment of the present invention provides a method that employs natural hydraulic cues.
Refer to FIGS. 1, 2, and 3. To protect fishes that are not intercepted by an SBC, or if an SBC is not available, the present state-of-the-art for fish protection uses diversion screens 206, 300 such as ones shown in FIGS. 2 and 3, to intercept fish and prevent them from entering intakes of turbines or diversion canals. For example, FIG. 1 illustrates typical structures commonly encountered by fish as they attempt to move from the forebay on the upstream side of a dam to downstream river reaches. The dam depicted consists of a powerhouse 101 and a spillway 102 with water flow indicated by arrows 103. Once the water passes the dam, it and its contents are dumped into the tailrace 104.
FIG. 2 shows design features (through cut 1-1 of FIG. 1) of a conventional system used to intercept outmigrating fish. A portion of the flow 103 and surface oriented fish pass through a trash rack 203 and some fish are intercepted by the diversion screen 206 and guided up into a gatewell 202. A barrier screen 201 returns the majority of the flow back into the turbine 204 for subsequent discharge through the draft tube 205 and concentrates the diverted fish in the gatewell 202. From the gatewell 202, outmigrating fish are collected using several different means and conveyed around the dam.
Refer to FIG. 3. There are three primary design criteria for diversion screens 300. The first is hydraulic efficiency, i.e., screens 300 should be designed to minimize energy loss across their surface, thereby maximizing energy potential for associated hydropower facilities. Second, screens 300 should be designed so that approach water velocity 103 is low enough so that fish do not impact the screen 300 at damaging velocities. The approach velocity 103 is partially controlled by a perforated plate 302 that is installed behind (downstream) of the screen surface 301. The size and spacing of the perforations 306 on the plate 302 may be adjusted to vary the water velocity approaching the screen surface 301. Third, the wires or bars 304 that constitute the screen surface area are spaced 303 so that fish of a certain minimum size are blocked by the screen 300 and physically prevented from passing through the screen 300. The flow pattern approaching the screen surface 301 is determined by the following characteristics of the system: discharge passing into the intake; the size and shape of the intake; the angle of deployment of the screen 300; the size, shape, and spacing of the bars 304 or wires that comprise the screen surface 301; the size, shape and location of structural members 304, 305 that make up the screen 300 frame; and the size and spacing of the perforations 306 in the back plate 302.
The design criteria for minimizing head loss can have significant effects on fish that approach the screen surface 301. Refer to FIG. 4. A byproduct of increased screen efficiency is that less of the energy of the water passing through the screen 300 is available to generate secondary hydraulic cues that fish can use to detect and avoid the screen surface 301. Therefore, as hydraulic efficiency increases the screen 300 becomes more hydrodynamically transparent so that fish become more likely to contact the screen surface 301 where they may be injured or killed. In response, the perforation plate 302 must be redesigned or other steps must be taken to decrease approach velocities 103.
A need, therefore, exists for an optimum method of guiding migrating fish, in particular juvenile fish, in a way that minimizes the propensity of fish to impact diversion screens. A further need exists to modify existing barriers to reduce the cost of implementing the optimum method.
A structure and method of adding natural hydrodynamic cues to manmade barriers in waterways is provided. It simulates those cues produced by the flow of water over rough streambeds. Fauna, such as fish, detect the cues and avoid high velocity impact on the barrier surface in the same way that they avoid collision with natural, solid features of the streambed.
The method that thus assists waterborne fauna adds at least one feature to existing barriers (or conventional barrier designs) that enables simulation of natural hydraulic cues of which fauna are receptive. The simulated cue initiates an instinctive awareness in the fauna, e.g., migrating juvenile fish, to detect and thereby avoid barriers such as fish diversion screens at a dam. The absence of such a feature may result in the fauna contacting barriers at harmful velocities.
For conventional fish diversion screens, adding a feature comprises affixing rows of elements to the downstream side of the diversion screens. The elements, such as rectangular plates are arranged with a longest dimension approximately perpendicular to the longest dimension of the material that comprises the diversion screens, e.g., wire or bars. The plates are affixed to the diversion screens across their thickness in spacing and dimension by using standard engineering methods that may also accommodate requirements not related to simulating the natural hydraulic cue. A convenient location for affixing the plates on conventional diversion screens is at the U-clips that both locate (space) and connect the wires or bars used to construct the planar diversion screen.
The diversion screen that results from incorporating a preferred embodiment of the present invention in a conventional design generates a natural hydraulic cue that permits fauna to avoid contact with the screen. It may be built from material such as parallel wires or bars that are much longer in one dimension than in any other dimension, and much smaller in its smallest dimension than in any other dimension, such as a thin rectangular plate. A series of connectors, such as U-clips, connect the existing elements of a conventional diversion screen in parallel, in accordance with a pre-specified spacing assigned between the smallest dimension (thickness) of each element. This yields a planar structure, i.e., a screen, with a minimum pre-specified spacing between any two elements. So far a conventional diversion screen has been described. A second series of parallel elements, such as rectangular plates, is affixed on the downstream side of the planar structure proximate the connectors (U-clips in some designs). Orienting these rectangular plates approximately perpendicular to the longest dimension of the bars or wires of the screen, affixed on edge to the conventional diversion screen, enables a natural cue to be generated by the heretofore conventional screen design in the sense that the resulting upwelling resembles water flowing over a rock or other channel feature.
Conveniently, existing barriers or screens may be modified using a preferred embodiment of the present invention. Affixing a configuration in accordance with the present invention enables a diversion screen to generate a natural cue for receipt by fauna otherwise susceptible to harmful impact on barriers such as fish diversion screens. The configuration is attached to a downstream side of a barrier or diversion screen in such a manner that the resultant Natural Cue Diversion Screen (NCDS) creates localized, dynamic hydraulic features simulating those features that fauna use to instinctively avoid natural barriers in waterways. A proper distribution of elements, such as rectangular plates, on the downstream side of the diversion screen provides a pattern of natural hydraulic cues across the entire surface of the diversion screen. The plates may also replace a perforated back plate of a conventional design, thus performing double duty by reducing the flow of water through a surface of the diversion screen to a predetermined quantity.
A preferred embodiment of the present invention provides a design that enables the generation of natural hydraulic cues. In one embodiment, modifying existing conventional fish diversion screens, the modification adds a series of rectangular plates attached to U-clips. These U-clips are welded on the bottoms of the bars or wire of the conventional screen for structural support and spacing of the individual bars that are the basic elements of the screen. The plates are oriented so that they are approximately perpendicular to the flow lines approaching and passing through the screen surface. A portion of the flow collides with the plates to create locally unstable hydraulic features that chaotically slip above and below the plates. This chaotic hydrodynamic oscillation extends above the screen surface and can be detected by fish prior to a possible relatively high velocity contact with the screen surface. Fish are thereby guided by the signals generated by the modified screen thus reducing unheralded collisions with the screen surface or supporting structure.